The present invention generally relates to switches for asynchronous transfer mode (ATM) networks. In particular, the present invention relates to distributed ATM switches for use within an ATM network including processing satellite links.
ATM networks may provide substantial performance increases over more traditional time division multiplexing (TDM) networks (also known as synchronous transfer mode or STM networks). This is especially true when the networks must carry many different types of information (e.g., data, voice, and video). Information travelling over an ATM network is coded into 53-byte cells. The first 5 bytes of each cell are the cell header and contain important information about the cell, including the routing information (i.e., destination address) for the cell.
In ATM, a transmission path (TP) is a set of physical connections that link the network. Virtual paths and virtual circuits are mappings laid over the TPs that control the flow of cells from sending terminals to receiving terminals. A virtual path represents a set of TPs assigned to carry cells that share higher-order address bits. Virtual paths contain one or more virtual circuits. A virtual circuit represents a set of TPs assigned to carry cells that share lower-order address bits. A virtual path may generally be thought of as a bundle of one or more virtual circuits. An assignment of a virtual path and a virtual circuit defines a virtual connection (VC) between any two network elements.
An important concept in ATM is that of the service contract. A service contract is an agreement between a user and the network that establishes certain parameters that the user will follow. For example, the contract may specify a certain average data rate the user is to maintain when sending data over the network. A service contract will also specify the quality of service (QoS) that the network will maintain with respect to the connection between any two user terminals. A QoS class defines parameters that represent a minimal level of network performance for the traffic carried by links that are designated as providing that particular QoS. Thus, for any two network elements within a network, there may need to be as many VCs set up between them as there are QoS classes defined for that network.
An ATM network may be envisioned as a sending user terminal, a receiving user terminal and an ATM cloud. The sending user terminal is connected to the cloud. The first switch through which the user terminal traffic passes after entering the cloud is said to serve as a user-network interface (UNI) with respect to that terminal. At a UNI, a function known as Usage Parameter Control (UPC) is performed. The UPC function ensures that the user terminal sending data into the ATM cloud is not exceeding the service parameters of its contract. For example, the UPC function determines whether or not a user terminal is sending data at a rate above the average bit rate established as set forth in its contract.
ATM switch functions are typically divided into user plane functions and control plane functions. User plane functions are those functions that control the movement of cells across the switch. A typical user plane function, for example, is the UPC function for established VCs. Control plane functions are typically those which relate to connection establishment and overall management of traffic flow. Some typical control plane functions include, for example, connection admission control (CAC) and routing (the selection of appropriate TPs for a particular VC).
As noted above, the UPC policing function ensures that a user terminal is not exceeding the usage requirements of the contract under which it was established. If the policing function determines that a user terminal is exceeding its allowed rate, then it checks to see if the guaranteed QoS can be met for all other contracts in existence. As long as the established QoS can be maintained for all contracts, the UNI may allow the additional traffic. However, if the established QoS for all other contracts can not be maintained, then the cells may be dropped. One problem with the occurrence of such a cell drop is that the user is often unaware that it has occurred unless the receiving end informs the user that something is wrong.
In terrestrial ATM networks, the policing function is performed by the ATM switch that is serving as the UNI for the sending user terminal. However, this can be problematic when the first switch within the cloud is a satellite based switch. First, it necessitates additional processing equipment on the satellite. This adds space, weight and additional power requirements to the satellite design. A second problem is additional inefficiency. The policing function may cause cells to be dropped at times. If that decision is made in the satellite, uplink bandwidth is used to transmit cells that will never reach the downlink. Waste of uplink bandwidth is a waste of a very precious system resource.
Another important user plane function provided by the user terminal is user equipment interface adaptation. An example of this adaptation is the protocol translation from Ethernet to ATM.
An important control plane function is call admission control. This function makes the determination as to whether or not a call can be admitted given the traffic currently present in the network. Ideally, it makes a real time determination as to the feasibility of accepting a new call, while maintaining the requirements of all contracts. Putting this functionally within a satellite payload is again problematic because of the additional size, weight and power requirements.
Another control plane function is that of bandwidth allocation. It is similar to call admission control but operates on a shorter time scale such as that of individual cells. The bandwidth allocation function may be implemented on the payload, in the network operation center, or a combination of both.
A need has long existed in the industry for a distributed ATM network switch that is suitable for use within ATM networks that include processing satellite links.
It is an object of the present invention to provide a distributed ATM switch adapted to perform in an ATM network including processing satellite links.
Another object of the present invention is to provide an ATM switch that reduces the additional space, weight, and power requirements of ATM switch functionality in a satellite payload.
Yet another object of the present invention is to provide an ATM switch that conserves uplink bandwidth.
Still another object of the present invention is to provide an adaptive ATM switch for use in a network including processing satellite links.
One or more of the foregoing objects are met in whole or in part by a preferred embodiment of the present invention, which provides a distributed ATM switch. The functionality of the distributed ATM switch is preferably performed at three distinct locations. The first location is at a user earth terminal configured to perform at least one user plane function. The second location is at a network operations center configured to perform at least one control plane function. Finally, the remaining ATM switch functionality is performed within the payload of a processing satellite.